Adhesive alpha-olefin inter-polymers, adhesive compositions or formulations comprising such inter-polymers for adhesive application and adhesion processes and articles in which adhesive compositions or formulations are used.
Certain alpha-olefin inter-polymers have been used in adhesive compositions which should yield a significant bond strength after application, show good paper adhesion (e.g. fiber tear on Kraft paper), minimum peel strength of 500 g/cm, low color, low odor, and good thermal stability. For PSA applications, when the substrate is an OPP tape, the rolling ball tack test should yield a maximum of 3 cm at ambient temperature, a S.A.F.T. minimum value of 85xc2x0 C., a shear (12.5 mmxc3x9725 mm area under a 1 Kg weight) on cardboard at 40xc2x0 C. of at least 30 hours. Most known alpha-olefin inter-polymers in such compositions have a high melting point and/or a high crystallinity. These characteristics prevent such materials, on their own, from being used as an adhesive because an adhesive must a low crystallinity for flexibility and a low plateau modulus, as well as a low viscosity in many applications. (see J. Adhesion Sci. Technol. Vol 3, No 7 pp551-570 (1989) where an SBS block-copolymer is used).
In such prior art adhesive formulations, the alpha-olefin inter-polymers contribute to the bond-strength, but tackifiers are used to increase the Tg for good bond strength and bring the high plateau modulus down to an acceptable level by decreasing the polymer chain entanglements. Flow promoters (waxes etc) are used to improve the flow and ensure wetting of the substrate by the formulation. Without tackifiers and flow promoters, such inter-polymers can be used to heat seal at reduced temperatures but are not, generally, regarded as adhesives.
The inter-polymers are derived predominantly from ethylene or propylene (For ethylene based polymers see WO97-15636-A1; WO99/24516; WO9803603 (EP-912646) by way of example using single site catalyst; WO97-15636-A1 or WO94/10256; U.S. Pat. No. 5,317,070 and WO94/04625, using syndiotactic polypropylene as the polymer component, and mentioning on page 7 line 14 of hexene as comonomer. For propylene based polymers further see EP-318049. For basic monomers other than propylene or ethylene, see for example EP-422498 a butene-propylene inter-polymer with up to 20 wt % propylene derived units).
As an example of the inter-polymers used for heat sealing or impact modification, reference is made to JP62-119212-A2. This discloses a random copolymer with from 40-90 mole % of propylene, from 10-60 mole % of an alpha-olefin such as butene, hexene, and 4-methylpentene using a metallocene type ethylene-bis tetrahydro-indenyl zirconium dichloride as a catalyst. Similarly JP62-119213-A2 discloses a random copolymer of butene (60-98 mole %) with 2-40 mole % of C3-20 alpha-olefin such as propylene, hexene, and 4-methylpentene.
However, the Examples in JP62-119212-A2 have widely varying characteristics. Example 6 polymerizes propylene and hexene to give 60 percent of units derived from propylene and 40 mol % of units derived from hexene. The crystallinity is 26% and the melting point is 123xc2x0 C. Example 3 uses propylene at 45 mol % with a melting point of 50xc2x0 C. and a crystallinity 7%. JP62-119212-A2 does not disclose a polymer having a combination of structural characteristics (molecular weight; comonomer content for example) such that a storage modulus Gxe2x80x2 suitable for adhesive applications is reached below 70xc2x0 C. or providing a low melting peak. The polymers are said to have anti-blocking characteristics and are of no use in adhesive applications.
WO99/67307 discloses a terpolymer comprising predominantly propylene derived units for use as films, fibers, and molded articles, and also seal layers. The polymers in Table 4 have low comonomer contents, high melting points and high molecular weights.
WO9920644 discloses elastic composition of propylene homopolymers for adhesive application. Metallocenes are used in the polymerization.
In other documents, alpha-olefin inter-polymers are prepared using a conventional Ziegler-Natta catalyst with a titanium chloride transition metal component and an aluminum alkyl activator to give a polymer with a monomer composition in which the amounts of propylene (lower molecular weight comonomer) and higher molecular weight comonomer are approximately equivalent have been suggested for adhesive application. These have been referred to as A(morphous) P(oly) A(lpha) O(lefin), APAO""s for short.
U.S. Pat. No. 3,954,697 discloses in example 1 a propylene-hexene-1 copolymer containing 43 mol % of hexene-1 derived units which can be coated onto a tape hot to give a pressure sensitive adhesive material. The polymer may be used without additives (See column 2 lines 34 to 39) and can be applied as a hot melt to a tape without solvent to show PSA behavior. In U.S. Pat. No. 3,954,697, the amount of hexene deemed essential for a polymer is in excess of 40 mol % and the polymer structure must be such that that the polymer is entirely amorphous and has no residual crystallinity (See Column 3 lines 24 to 26) or crystallinity of a very low order (See column 4 line 8). For example, comparative Example 9 uses 18 mol % hexene in the polymer and obtains a melting point of 145xc2x0 C. suggesting the absence of Theological characteristics or melting points associated with satisfactory adhesive behavior. This polymer lacks tackiness at ambient temperature.
High propylene content APAO with butene comonomer have been made and sold under the Registered trade name Rextac using non-SSC type catalysts. WO98/42780 discusses the use of such polymers in adhesive compositions.
More details on such inter-polymers and their use in adhesive compositions can be found in U.S. Pat. No. 5,478,891. U.S. Pat. No. 5,723,546 uses blends to obtain the desired characteristics. Details can be derived from U.S. Pat. No. 4,217,428, U.S. Pat. No. 4,178,272 and U.S. Pat. No.3954697 which recommend generally high amounts of the higher molecular weight alpha-olefin comonomer.
WO9823699 and EP 620257 disclose a polymer in which from 70 to 99 mol % is derived from a C6 to C12 alpha-olefin and the remainder is a lower alpha-olefin. The exemplified combinations are of hexene-propylene and octene-ethylene inter-polymers prepared with a conventional Ziegler-Natta catalyst. A low Tg can be obtained. The material may be cross-linked to improve cohesive strength. Nevertheless there are drawbacks associated with such polymers and their application in adhesive end uses. Such known APAO""s are non-homogenous, have significant levels of extractables and unsatisfactory physical properties, including low cohesive strength, that restrict the application and adhesive performance.
The invention relates (I) to novel adhesive alpha-olefin inter-polymers which are largely amorphous and have a Theological behavior that makes them suitable for adhesive use. In this aspect, the invention also relates to processes for the manufacture of these adhesive alpha-olefin inter-polymers.
In one aspect the invention provides a polymer which is suitable for adhesive use and has a sufficiently high storage modulus upon cooling, without relying unduly on the presence of lower molecular weight components such as a tackifier (which can create problems of excessive migration of its constituents and requires blending) or low molecular impurities formed in the course of polymerization and/or which has a low melting point with a narrow melting range and/or which has a monomer distribution pattern which provides an improved balance of low melting point and cohesive strength. Therefore in one aspect the invention provides an adhesive composition or formulation which contains no or low amounts of tackifier, yet provides a satisfactory balance of properties for an adhesive composition.
Advantages of the invention include improved polymers which can be used with reduced amounts of, or possibly no tackifier, in order to provide a hot melt adhesive composition or formulation. These polymers can be used with reduced amounts of, or possibly no solvent, in order to provide a adhesive formulations with reduced environmental impact. Further, another embodiment of the invention provides sprayable adhesive formulations, including sprayable HMA compositions, comprising predominantly of polymers having a reduced plateau modulus and/or molecular weight.
In one specific embodiment the invention provides in a first aspect a poly-alpha olefin inter-polymer comprising
A) from 60 to 94mol % of units derived from one alpha mono-olefin having from 3 to 6 carbon atoms and
B) from 6 to 40 mol % of units derived from one or more other mono-olefins having from 4 to 10 carbon atoms and at least one carbon atom more than A); and
C) optionally from 0 to 10 mol % of units derived from another copolymerizable unsaturated hydrocarbon, different from A) and B);
the diad distribution of component A in the polymer as determined by 13C NMR as described herein showing a ratio of experimentally determined diad distribution over the calculated Bemoullian diad distribution of less than 1.07; and
the storage modulus Gxe2x80x2 of said polymer, determined upon cooling as described herein, intersecting a value of 3.105 Pa at a temperature of less than 85xc2x0 C.
In another aspect there is provided a poly-alpha olefin inter-polymer having (I)
A) from 60 to 94mol % of units derived from one alpha mono-olefin having from 3 to 6 carbon atoms and
B) from 6 to 40 mol % of units derived from one or more other mono-olefins having from 4 to 10 carbon atoms and at least one carbon atom more than A); and optionally from 0 to 10 mol % of units derived from another copolymerizable unsaturated hydrocarbon, different from A) and B);
the diad distribution of component A in the polymer as determined by 13C NMR as described herein showing a ratio of experimentally determined diad distribution over the calculated Bemoullian diad distribution of less than 1.07; and
said polymer having a melting behavior as determined by DSC, as described herein, so that Tm (interpolymer) is less than 153xe2x88x922.78 xc3x97[CB+C] for any given concentration of B) and/or C) components where Tm is the major melting peak of the interpolymer at a given content of components B) and C) in mol %; [CB+C] is the mol % of component B) plus C).
The invention thus further relates (II) to adhesive compositions which consist predominantly of the inter-polymer and to formulations for adhesive end-uses comprising the inter-polymer and in addition limited amounts of other components such a) tackifiers for lowering the plateau modulus and/or b) flow promoters such as low molecular weight additives for lowering the viscosity of the formulation in its molten state during the application of the formulations onto a substrate. Anti-oxidants, stabilisers etc. may also be present in the composition and formulations.
Such compositions or formulations may be a hot melt adhesive (HMA) and be applied to a substrate in the substantial absence of solvent or diluent at above ambient temperature to initiate adhesion and then cool to ambient temperature to establish a bond.
Such compositions or formulations may be a pressure sensitive adhesive (PSA) and be applied in the substantial absence of solvent or diluent to a substrate to initiate adhesion at ambient temperature. If the PSA is applied hot to its substrate to form an article, for example a tape or label which is subsequently used at ambient temperature to initiate adhesion, the PSA is known as a hot melt pressure sensitive adhesive (HMPSA).
Such compositions or formulations may be applied as a solution in the presence of a suitable solvent for the components, to give a solvent based adhesive (SBA). Such solutions are applied to substrate and the solvent is evaporated. For example, the adhesive layer then acts similarly to the HMPSA and is called a solvent-based pressure sensitive adhesive (SBPSA).
The invention additionally relates (III) to processes using such compositions or formulations as well as articles obtained by such processes. For example the compositions and formulations of the invention can be sprayed, preferably in filamentary form, onto a substrate for use in packaging and for disposable items, such as diapers, and other sanitary articles or can be used for adhesive tape.